Hermetically sealed semiconductor devices as referred to above, such as solid state image sensing devices, photosensors or ultraviolet erasable EP-ROM, generally have a box-core hollow resin molded item, a lead frame, a semiconductor chip, bonding wires and a covering member.
Generally, such hermetically sealed semiconductor devices as mentioned above are produced hitherto by a so-called insert molding technique wherein a lead frame is first embedded in a mold and the lead frame is then integrated with a core-box hollow resin molded item by means of a resin which is injection or transfer molded in the mold.
In the insert molding technique, however, there was involved such a problem that because flashes of the resin are formed on the surface of the lead frame during the molding process, electrical connection between the lead frame and semiconductor element cannot be attained satisfactorily with ease.
In order to solve the above-mentioned problem, there has generally been adopted a process wherein a semiconductor element is electrically connected in advance onto a lead frame, followed by resin molding.
In this process, however, there was involved such a problem that functions of the semiconductor element is liable to be impaired, because the element is subjected to elevated temperature and impact at the time of molding.
Furthermore, there have been made various attempts to facilitate electrical connection between the lead frame and semiconductor element. For instance, such attempts include a procedure for removing the flashes by blasting abrasive grains, a procedure for dissolving and delaminating the flashes by using chemicals, and a procedure for removing the flashes by using a jet of liquid at high pressure (Japanese Patent L-O-P Publn. No. 1502033/1985).
In the above-mentioned blast finishing procedure, however, there was involved such a problem that because the surface of the resin molded section is damaged by blasting, said surface must be masked during the blasting and hence the production process becomes complicated. In the procedure using chemical, there was involved the same problem as in the case of the above-mentioned blast finishing procedure, that is, the flashes cannot be removed perfectly even though said flash can be delaminated and hence a further brushing procedure is required for perfectly removing the flashes, resulting in damage of the surface of the resin molded section. Furthermore, in the procedure using a jet of liquid at high pressure, there was involved such a problem that the use of a high pressure liquid jetting device of sophisticated structure having two jet nozzles is imperatively needed for removing the flashes attached to both surfaces of the lead frame.
In practicing the above-mentioned insertion molding, occurrence of foreign particles resulting from fillers contained in plastics or of foreign particles resulting from flashes of plastics is unavoidable, and if this condition proceeds, as it is, to the subsequent step, such foreign particles present will attach to the inner surface of a covering member of semiconductor device or to the surface of semiconductor element during said subsequent step. On that account, there is brought about such a serious problem that images appear with a noise or transmittance of ultraviolet ray decreases in such a semiconductor device as an image sensor using quartz plate or sapphire plate as a covering member of the semiconductor device or EP-ROM (Erasable and Programmable Read Only Memory).
In hermetically sealed semiconductor devices obtained by the above-mentioned insertion molding technique, moreover, there was involved such a problem that if adhesion between a lead frame and a core-box hollow resin molded item is poor, exterior humidity permeates inside the core-box hollow resin molded item through an adhesive interface between the lead frame and core-box hollow resin molded item and thereby causing a trouble of semiconductor element present therein, and thus the resulting semiconductor devices are found to be less reliable.
As a measure to solve such problems mentioned above, it has heretofore been known to prepare a core-box hollow resin molded item by using resins improved in physical properties or to use a lead frame treated with certain kinds of chemicals. For instance, there are processes in which a core-box hollow resin molded item equipped with a lead frame is formed by using a resin incorporated with a rubber component so that an internal stress of the resulting core-box hollow resin molded item is reduced, and thereby to improve adhesion between the core-box hollow resin molded item and the lead frame, a process in which a core-box hollow resin molded item equipped with a lead frame is formed by using a resin incorporated with a silane coupling agent, and thereby to improve adhesion between the core-box hollow resin molded item and the lead frame, and a process in which a core-box hollow resin molded item equipped with a lead frame is formed by using the lead frame treated with a silane coupling agent, and thereby to improve adhesion between the lead frame and the core-box hollow resin molded item.
All the processes as mentioned above, however, involved such a problem that moldability, particularly releasing characteristics, of the resin used is unsatisfactory. Further, the process using the lead frame treated with the silane coupling agent involved such a problem that said process becomes complicated.